1. Field of the Invention
The present invention relates generally to a shutter driving system for a camera, and more particularly to a shutter driving system that provides for accurate automatic focusing.
2. Description of Related Art
A proposed camera has a lens shutter driven by a fast motor of a diaphragm and shutter for a suitable exposure amount includes combined shutter blades and diaphragm, an opening lever for opening or closing the shutter blades at a closing position of a shutter opening and a diaphragm set position, a diaphragm ring having a cam portion for setting an operation position of the opening lever in advance, a driving ring followed by an operation of the opening lever and having a steeply slant face by the cam portion, a motor for operating the diaphragm ring and the driving ring, additionally a ratchet for an automatic focusing, and an engagement lever for locking the ratchet by an armature selectively attracted to an electromagnet.
In this proposed camera, automatic focusing is performed by locking the diaphragm ring after the electromagnet is magnetized when the diaphragm ring is operated by the driving ring rotated in response to a forward rotation of the motor and comes to a calculated number. The driving ring is rotated clockwise in accordance with an F number set in advance in accordance with a rearward rotation of the motor, and the opening lever is operated by the cam portion having the steeply slant face, thereby an automatic exposing can be embodied.
Since the engagement lever for locking the ratchet is locked in one step per one pitch in response to an ON/OFF operation of the armature, and rebound impact power is caused by a spring when the automatic focusing is carried out, it is difficult to secure the exact focusing position. In addition, since a shutter open time is decided by the driving ring having the cam portion with the steeply slant face contacting the opening lever for controlling the operation of the shutter blades, a response speed of the opening lever for controlling an opening or closing time of the shutter blades is delayed, such that a clear image of an object can be obtained as the shutter open state is maintained for a long period of time.